Method and system for predictive physiological gating of radiation therapy

ABSTRACT

A method and system for physiological gating for radiation therapy is disclosed. A method and system for detecting and predictably estimating regular cycles of physiological activity or movements is disclosed. Another disclosed aspect of the invention is directed to predictive actuation of gating system components. Yet another disclosed aspect of the invention is directed to physiological gating of radiation treatment based upon the phase of the physiological activity.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.09/178,383, filed Oct. 23, 1998 now U.S. Pat. No. 6,621,889 the entiredisclosure is expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to medical methods and systems. Moreparticularly, the invention relates to a method and system forphysiological gating of radiation therapy.

2. Background

Radiation therapy involves medical procedures that selectively exposecertain areas of a human body, such as cancerous tumors, to high dosesof radiation. The intent of the radiation therapy is to irradiate thetargeted biological tissue such that the harmful tissue is destroyed. Incertain types of radiotherapy, the irradiation volume can be restrictedto the size and shape of the tumor or targeted tissue region to avoidinflicting unnecessary radiation damage to healthy tissue. For example,conformal therapy is a radiotherapy technique that is often employed tooptimize dose distribution by conforming the treatment volume moreclosely to the targeted tumor.

Normal physiological movement represents a limitation in the clinicalplanning and delivery of conventional radiotherapy and conformaltherapy. Normal physiological movement, such as respiration or heartmovement, can cause a positional movement of the tumor or tissue regionundergoing irradiation. If the radiation beam has been shaped to conformthe treatment volume to the exact dimensions of a tumor, then movementof that tumor during treatment could result in the radiation beam notbeing sufficiently sized or shaped to fully cover the targeted tumoraltissue.

One approach to this problem involves physiological gating of theradiation beam during treatment, with the gating signal synchronized tothe movement of the patient's body. In this approach, instruments areutilized to measure the physiological state and/or movement of thepatient. For example, respiration has been shown to cause movements inthe position of a lung tumor in a patient's body. If radiotherapy isbeing applied to the lung tumor, then a temperature sensor, straingauge, preumotactrograph, or optical imaging system can be utilized tomeasure the patient's respiration cycle. These instruments can produce asignal indicative of the movement of the patient during the respiratorycycle. The radiation beam can be gated based upon certain thresholdamplitude levels of the measured respiratory signal, such that theradiation beam is disengaged or stopped during particular time points inthe respiration signal that correspond to excessive movement of the lungtumor.

Known approaches to physiological gating of radiation therapy arereactive, that is, known approaches utilize gating methods thatslavishly react to measured levels of physiological movements. Onedrawback to reactive gating systems is that the measured physiologicalmovement may involve motion that that is relatively fast when comparedto the effectively operating speeds of gating system components. Thus, apurely reactive gating system may not be able to react fast enough toeffectively gate the applied radiation. For example, the gating systemmay include a switch for gating the radiation treatment, in which theswitch requires a given time period Δt to fully engage. If the switchingtime period Δt is relatively slow compared to the measured physiologicalmotion cycle, then a system employing such a switch in a reactive mannermay not be able to effectively gate the application of radiation atappropriate time points during the radiation therapy.

Therefore, there is a need for a system and method to address these andother problems of the related art. There is a need for a method andsystem for physiological gating which is not purely reactive to measurephysiological movement signals.

SUMMARY OF THE INVENTION

The present invention provides an improved method and system forphysiological gating for radiation therapy. According to an aspect, theinvention comprises a method and system for detecting and predictablyestimating regular cycles of physiological activity or movements.Another aspect of the invention is directed to predictive actuation ofgating system components. Yet another aspect of the invention isdirected to physiological gating of radiation treatment based upon thephase of the physiological activity.

These and other aspects, objects, and advantages of the invention aredescribed below in the detailed description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention and, together with the DetailedDescription, serve to explain the principles of the invention

FIG. 1 depicts the components of a system for physiological gatingaccording to an embodiment of the invention.

FIG. 2 depicts an example of a respiratory motion signal chart.

FIG. 3 depicts a motion signal chart and a gating signal chart.

FIG. 4 is a flowchart showing process actions performed in an embodimentof the invention.

FIG. 5 is a flowchart showing process actions for detecting andpredicting estimation of regular physiological movements.

FIG. 6 a depicts a side view an embodiment of a camera that can beutilized in the invention.

FIG. 6 b depicts a front view of the camera of FIG. 6 a

FIG. 7 a depicts a retro-reflective marker according to an embodiment ofthe invention.

FIG. 7 b depicts a cross-sectional view of the retro-reflective markerof FIG. 7 a

FIG. 8 depicts an apparatus for making a retro-reflective marker.

FIG. 9 depicts a phase chart synchronized with a gating signal chart.

FIG. 10 depicts an embodiment of a cylindrical marker block.

FIG. 11 depicts an embodiment of a hemispherical marker block

FIG. 12 is a diagram of a computer hardware system with which thepresent invention can be implemented.

DETAILED DESCRIPTION

An aspect of the present invention comprises a method for detecting andpredictively estimating regular cycles of physiological activity ormovement. The method of the invention can be employed for any regularphysiological activity, including for example, the respiratory orcardiac cycles.

In operation, one or more sets of data representative of thephysiological activity of interest are collected for the patient. Forexample, an electrocardiograph can be employed to generate datarepresentative of the cardiac cycle. To generate data representative ofthe respiration cycle, a temperature sensor, strain gauge orpreumotactrograph can be employed. Other instruments or mechanisms canbe employed within the scope of the invention to obtain sets of datarepresentative of physiological activity or movements.

FIG. 1 depicts the components of an embodiment of a system 100 forphysiological gating of radiation therapy, in which data representativeof physiological activity is collected with an optical imagingapparatus. System 100 comprises a radiation beam source 102 (such as aconventional linear accelerator) which is positionally configured todirect a radiation beam at a patient 106 located on treatment table 104.A switch 116 is operatively coupled to the radiation beam source 102.Switch 116 can be operated to suspend the application of the radiationbeam at patient 106. In an embodiment, switch 116 is part of themechanical and electrical structure of radiation beam source 102.Alternatively, switch 116 comprises an external apparatus that isconnected to the control electronics of radiation beam source 102.

An optical or video image apparatus, such as video camera 108, is aimedsuch that as least part of the patient 106 is within the camera's fieldof view. Camera 108 monitors patient 106 for motion relating to theparticular physiological activity being measured. For example, ifrespiration movements of the patient is being monitored, then camera 108can be configured to monitor the motion of the patient's chest.According to an embodiment, camera 108 is placed with its axis atapproximately 45 degrees to the longitudinal axis of the patient 106.For measurement of respiration activity that could result in about 3-5mm of chest motion, the video image field of view is preferably set toview an approximately 20 cm by 20 cm area of the patient's chest. Forpurposes of illustration only, a single camera 108 is shown in FIG. 1.However, the number of cameras 108 employed in the present invention canexceed that number, and the exact number to be used in the inventiondepends upon the particular application to which it is directed.

In an embodiment, one or more illumination sources (which are infraredsources in the preferred embodiment) project light at the patient 106 ontreatment table 104. The generated light is reflected from one or morelandmarks on the patient's body. The camera 108, which is directed atpatient 106, captures and detects the reflected light from the one ormore landmarks. The landmarks are selected based upon the physiologicalactivity being studied. For example, for respiration measurements,landmarks are selected from one or more locations on the patient'schest.

The output signals of camera 108 are sent to a computer 110 or othertype of processing unit having the capability to receive video images.According to a particular embodiment, computer 110 comprises an IntelPentium-based processor running Microsoft Windows NT and includes avideo frame grabber card having a separate channel for each video sourceutilized in the system. The images recorded by camera 108 are sent tocomputer 110 for processing. If camera 108 produces an analog output,the frame grabber converts the camera signals to a digital signal priorto processing by computer 110. Based upon the video signals received bycomputer 10, control signals can be sent from computer 110 to operateswitch 116.

According to one embodiment, one or more passive markers 114 are locatedon the patient in the area to be detected for movement. Each marker 114preferably comprises a reflective or retro-reflective material that canreflect light, whether in the visible or invisible wavelengths. If theillumination source is co-located with camera 108, then marker 114preferably comprises a retro-reflective material that reflects lightmostly in the direction of the illumination source. Alternatively, eachmarker 114 comprises its own light source. The marker 114 is used inplace of or in conjunction with physical landmarks on the patient's bodythat is imaged by the camera 108 to deteot patient movement. Markers 114are preferably used instead of body landmarks because such markers 114are easier to detect and track via the video image generated by camera108. Because of the reflective or retro-reflective qualities of thepreferred markers 114, the markers 114 inherently provide greatercontrast in a video image to a light detecting apparatus such as camera108, particularly when the camera 108 and illumination source areco-located.

Utilizing a video or optical based system to track patient movementprovides several advantages. First, a video or optical based systemprovides a reliable mechanism for repeating measurement results betweenuses on a given patient. Second, the method of the invention isnoninvasive, and even if markers are used, no cables or connections mustbe made to the patient. Moreover, if the use of markers is impractical,the system can still be utilized without markers by performingmeasurements of physiological activity keyed to selected body landmarks.Finally, the method of the invention is more accurate because it isbased upon absolute measurement of external anatomical physicalmovement.

A possible inefficiency in tracking the markers 114 is that the markermay appear anywhere on the video frame, and all of the image elements ofthe video frame may have to be examined to determine the location of themarker 114. Thus, in an embodiment, the initial determination oflocations for the marker 114 involves an examination of all of the imageelements in the video frame. If the video frame comprise 640 by 480image elements, then all 307200 (640*480) image elements are initiallyexamined to find the location of the markers 114.

For real-time tracking of the marker 114, examining every image elementfor every video frame to determine the location of the marker 114 inreal-time could consume a significant amount of system resources. Thus,in an embodiment, the real-time tracking of marker 114 can befacilitated by processing a small region of the video frame, referred toherein as a “tracking gate”, that is placed based on estimation of thelocation of the already identified marker 114 in the video frame. Thepreviously determined location of a marker 114 defined in the previousvideo frame is used to define an initial search range (i.e., thetracking gate) for that same marker in real-time. The tracking gate is arelatively small portion of the video frame that is centered at theprevious location of the marker 114. The tracking gate is expanded onlyif it does not contain the new location of the marker 114. As anexample, consider the situation when the previously determined locationof a particular marker is image element (50,50) in a video frame. If thetracking gate is limited to a 50 by 50 area of the video frame, then thetracking gate for this example would comprise the image elements boundwithin the area defined by the coordinates (25,50), (75,50), (50,25),and (50,75). The other portions of the video frame are searched only ifthe marker 106 is not found within this tracking gate.

The video image signals sent from camera 108 to computer 110 are used togenerate and track motion signals representative of the movement ofmarker 114 and/or landmark structures on the patient's body. FIG. 2depicts an example of a motion signal chart 200 for respiratory movementthat contains information regarding the movement of marker 114 during agiven measurement period. The horizontal axis represents points in timeand the vertical axis represents the relative location or movement ofthe marker 114. According to an embodiment, the illustrated signal inFIG. 2 comprises a plurality of discrete data points plotted along themotion signal chart 200.

An important aspect of physiological gating of radiotherapy is thedetermination of the boundaries of the “treatment intervals” forapplying radiation. For gating purposes, threshold points can be definedover the amplitude range of the motion signal to determine theboundaries of the treatment intervals. Motion of the patient that falloutside the boundaries of the treatment intervals correspond to movementthat is predicted to cause unacceptable levels of movement to the tumoror tissue targeted for irradiation. According to an embodiment, thetreatment intervals correspond to the portion of the physiological cyclein which motion of the clinical target volume is minimized. Otherfactors for determining the boundaries of the treatment intervalsinclude identifying the portion of the motion signals involving theleast movement of the target volume or the portion of the motion signalinvolving the largest separation of the target volume from organs atrisk. Thus, the radiation beam pattern can be shaped with the minimumpossible margin to account for patient movement

Radiation is applied to the patient only when the motion signal iswithin the designated treatment intervals. Referring to FIG. 3, depictedare examples of treatment intervals, indicated by signal range 302, thathas been defined over the motion data shown in motion signal chart 200.In the example of FIG. 3, any movement of the measured body locationthat exceeds the value of 0.8 (shown by upper boundary line 304) orwhich moves below the value of 0.0 (shown by lower boundary line 306)falls outside the boundaries of the treatment intervals.

Shown in FIG. 3 is an example of a gating signal chart 300 that isaligned with motion signal chart 200. Any motion signal that fallsoutside the treatment interval signal range 302 results in a “beam hold”gating signal threshold 310 that stops the application of radiation tothe patient. Any motion signal that is within the treatment intervalsignal range 302 results in a “beam on” gating signal threshold 312 thatallows radiation to be applied to the patient. In an embodiment, digitalsignals that represent the information shown in motion signal chart 200are processed by computer 110 and compared to the threshold levels ofthe treatment interval signal range 302 to generate gating signalthresholds 310 and 312. Alternatively, gating signal thresholds 310 and312 can be obtained by feeding analog motion signals to a comparator tobe compared with analog threshold signals that correspond to treatmentinterval signal range 302. In any case, gating signal thresholds 310 and312 are generated by computer 110 and are applied to the switch 116 thatcontrols the operation of radiation beam source 102 (FIG. 1) to stop orstart the application of a radiation beam at patient 106.

FIG. 4 is a flowchart of the process actions performed in an embodimentof the invention. The first process action is to define boundaries forthe treatment intervals over the range of motion signals to be detectedby a camera (402). As indicated above, any motion that fall outside theboundaries of the treatment intervals correspond to motion that ispredicted to result in unacceptable levels of movement of the tumor ortissue targeted for irradiation. An optical or video imaging system,such as a video camera, is used to measure the physiological motion ofthe patient (404), and the output signals of the optical or videoimaging system are processed to compare the measured motion signals withthe threshold boundaries of the treatment intervals (406).

If the motion signal is outside the boundaries of the treatmentintervals, then a “beam off” gating signal threshold is applied to aswitch that is operatively coupled to the radiation beam source (408).If the radiation beam source is presently irradiating the patient (410),then the switch setting is operated to hold or stop the radiation beam(411). The process then returns back to process action 406.

If the motion signal is within the boundaries of the treatmentintervals, then a “beam on” gating signal threshold is produced (412)and is applied to a switch that is operatively coupled to the radiationbeam source. If the radiation beam source is presently not being appliedto the patient (413), then the switch setting is operated to turn on orapply the radiation beam source to irradiate the patient (414). Theprocess then returns back to process action 406.

According to one embodiment, the radiation beam source can be disengagedif a significant deviation is detected in the regular physiologicalmovements of the patient. Such deviations can result from suddenmovement or coughing by the patient. The position and/or orientation ofthe targeted tissue may unacceptably shift as a result of thisdeviation, even though the amplitude range of the motion signal stillfalls within the boundaries of the treatment intervals during thisdeviation. Thus, detection of such deviations helps define theappropriate time periods to gate the radiation treatment.

The present invention provides a method for detecting and predictivelyestimating a period of a physiological activity. In effect, the presentinvention can “phase lock” to the physiological movement of the patient.Since the gating system phase locks to the movement period, deviationsfrom that period can be identified and appropriately addressed. Forexample, when gating to the respiratory cycle, sudden movement orcoughing by the patient can result in deviation from the detected periodof the respiration cycle. The radiation treatment can be gated duringthese deviations from the regular period. The present invention alsoprovides a method for predictively estimating the period of thesubsequent physiological movement to follow.

FIG. 5 is a process flowchart of an embodiment of the invention toperform predictive estimation and detection of regular physiologicalmovement cycles. In process action 502, an instrument or system (such assystem 100 from FIG. 1) is employed to generate data signalsrepresentative of the physiological activity of interest. In anembodiment, the data signals comprises a stream of digital data samplesthat collectively form a signal wave pattern representative of thephysiological movement under examination. A number of discretemeasurement samples are taken for the physiological activity during agiven time period. For example, in an embodiment of the inventiondirected towards respiratory measurement, approximately 200-210 datasamples are measured for each approximately 7 second time interval.

In process action 504, pattern matching analysis is performed againstthe measured data samples. In an embodiment, the most recent set of datasamples for the physiological signal is correlated against animmediately preceding set of data samples to determine the period andrepetitiveness of the signal. An autocorrelation function can beemployed to perform this pattern matching. For each new sample point ofthe physiological motion or physiological monitoring sensor signal, theprocess computes the autocorrelation function of the last n samples ofthe signal, where n corresponds to approximately 1.5 to 2 signalbreathing periods. The secondary peak of the autocorrelation function isthen identified to determine the period and repetitiveness of thesignal.

In an alternate embodiment, an absolute difference function is usedinstead of an autocorrelation function. Instead of secondary peak, asecondary minimum in the absolute difference is searched for. For eachhew sample point of the physiological motion or physiological monitoringsensor signal, the process computes the minimum absolute differencebetween the two sets of data over a range of overlapping data samples.The secondary minimum corresponds to the data position that best matchesthe recent set of data samples with the preceding set of data samples.

Yet another alternate embodiment performs a pattern matching based upona model of the physiological activity being measured. The model is adynamic representation of the physiological motion or physiologicalmonitoring sensor signal for that physiological activity. The latest setof data samples is matched against the model to estimate parameters ofthe repetitive process.

Pattern matching using the measured physiological signal (504) providesinformation regarding the degree of match, as well as a location of bestmatch for the repetitive process. If an autocorrelation function isemployed in process action 504, then the relative strength of secondarypeak provides a measure of how repetitive the signal is. A thresholdrange value is defined to provide indication of the degree of matchbetween the two sets of data samples. If the strength of the secondarypeak is within the defined threshold range (process action 508), thenthe degree of match indicates that the signal is repetitive, and thesecondary peak location provides an estimate of the signal period. If anabsolute difference function is used in process action 504, then therelative value of the secondary minimum provides a measure of howrepetitive the signal is. If the value of the secondary minimum meets adefined threshold range (508), then the degree of match indicates thatthe signal is repetitive, and the secondary minimum location provides anestimate of the signal period.

If the correlation value of the secondary peak or secondary minimum doesnot meet the defined threshold range, then a deviation from the regularphysiological activity is detected, thereby indicating an irregularityin the regular physiological movement of the patient (510). Thisirregularity could result, for example, from sudden movement or coughingof the patient. In an embodiment, this detected irregularity results inthe generation of a “beam hold” signal that suspends the application ofradiation at the patient.

If the degree of match indicates repetitiveness, the point of best matchis tested to determine if the period is within a reasonable range. Thelocation of the secondary peak or secondary minimum provides an estimateof the period of the physiological activity. In an embodiment, the pointof best match is compared to a threshold range (509). If the point ofbest match does not fall within the threshold range, than a deviationfrom regular physiological activity is detected (510). If the point ofbest match falls within the threshold range, then the signal is acceptedas being repetitive (512).

The estimate of the period based on the point of best match can be usedto predict the period and waveform parameters of the next set of datasamples for the signal (514). Note that process actions 504, 508, and509 test for repetitiveness based upon a plurality of data samples overa range of such samples. However, in some circumstances, a significantdeviation from normal physiological movement may actually occur withinthe new or most recent data sample(s) being analyzed, but because theoverall set of data samples indicates repetitiveness (e.g., because ofaveraging of absolute differences over the range of data samples beingcompared), process actions 504, 508, and 509 may not detect thedeviation. To perform a test for rapid deviation, the predicted valuefrom process action 514 is compared with the next corresponding datasample (515). If the predicted value does not match the actual datasample value within a defined threshold range, then deviation isdetected (510). If a comparison of the predicted and actual data samplevalues fall within the defined threshold range, then repetitiveness isconfirmed, and deviation is not detected for that data sample range(516).

In an embodiment, the first time the process of FIG. 5 is performed, thepattern matching process action (504) is performed over the entire rangeof data samples. Thereafter, the pattern matching process action can beperformed over a limited search interval, which is defined by theresults of the prior immediate execution of the process. For example,the predicted value from process action 514 can be used to define thelocation of the search interval for the next set of data samples.However, if process action 508, 509, and 514 detect deviation based uponanalysis of the initial search interval, then the search interval can beexpanded to ensure that a deviation has actually occurred. The processof FIG. 5 can be repeated with the increased search interval to attemptto find a point of best match outside of the initial search interval. Inan embodiment, this increased search interval comprises the entire rangeof data samples. Alternatively, the increased search interval comprisesonly an expanded portion of the entire range of data samples.

According to an embodiment of the invention, physiological gating can beperformed based upon the phase of the physiological activity, ratherthan its amplitude. This is in contrast to the example shown in FIG. 3,in which the amplitude of the physiological movement signal defines theboundaries of the treatment intervals for the application of radiation.

Referring to FIG. 9, depicted is an example of a chart 900 showing thephase progression of a physiological movement signal. Treatment intervalrange 902 have been defined over the phase chart 900. In the example ofFIG. 9, the boundaries of the treatment interval range 902 are definedby the phase of the detected signal. Radiation is applied to the patientonly when the phase of the physiological movement signal falls withinthe boundaries of the treatment interval range 902. FIG. 9 depictsexamples of treatment interval range 902 having boundaries that spanfrom 30 degrees to 300 degrees. Thus, the applied radiation to thepatient is suspended or stopped when the phase of the physiologicalmovement signal is between 301 degrees to 29 degrees.

Shown in FIG. 9 is a gating signal chart 906 that is aligned with phasechart 900. A “beam hold” signal threshold 910 results if the phase ofthe physiological movement signal falls outside the treatment intervalrange 902. A “beam on” signal threshold 912 results if the phase of thephysiological movement signal falls within the boundaries of thetreatment interval range 902. The “bear on” and “beam hold” signalthresholds 910 and 912 are applied to a switch 116 that operativelycontrols the operation of a radiation beam source 102 (FIG. 1). Ifradiation is being applied to the patient, application of the “beamhold” signal threshold 910 triggers switch 116 to suspend or stop theapplication of radiation. If radiation to the patient is not beingapplied, application of the “beam on” signal threshold 912 triggers theapplication of radiation to the patient.

The predictive qualities of the present invention permits operation of agating system even if the measured physiological movement involvesmotion that that is relatively fast when compared to the effectivelyoperating speeds of gating system components. As just one example,consider a gating system that includes a switch for gating the radiationtreatment, in which the switch requires a known time period Δt to fillyengage. If the switching time period Δt is relatively slow compared tothe measured physiological motion cycle, then a system employing such aswitch in a reactive manner may not be able to effectively gate theapplication of radiation at the patient.

The present invention allows predictive triggering of switch 116 tocompensate for the amount of time Δt required to fully engage theswitch. A predicted period for a physiological activity can be obtainedby employing the process of FIG. 5. A treatment interval range isdefined over a portion of the period of the physiological activity.Based upon the time Δt required to fully actuate the switch 116, theswitch 116 can be pre-actuated by this time period Δt prior to the timeof the boundary of the treatment interval, so that the time for fullactuation of the switch 116 coincides with the boundary of the treatmentinterval. Thus, the radiation can be effectively gated at the boundariesof the treatment interval, regardless of the operating speeds of theswitch 116. The same procedure can also be employed to compensate forthe operating speeds of other gating system components.

The following is an embodiment of the invention coded in the VisualBasic programming language. The following program code is directed to aprocess for detecting and predictively estimating the respiration cycleperiod using the absolute difference function:

Public Function Predict(ByVal i As Long, ByVal Range As Long, Period AsDouble, MinAbsDiff As Double, Diff As Double) As Double Dim j As Long,StartJ As Long, CurrJ As Long Dim k As Long, MaxK As Long Dim AbsDiff AsDouble Dim NormAbsDiff As Double, n As Long k = Period − RangeMinAbsDiff = 10000000# StartJ = TimeRefIdxBuf((i − 201 + BufLength) ModBufLength) CurrJ = TimeRefIdxBuf((i − 1 + BufLength) Mod BufLength) Do j = StartJ  AbsDiff = 0#  n = 0  Do AbsDiff = AbsDiff +Abs(SigBuf(SigRefIdxBuf(j)) − SigBuf(SigRefIdxBuf((j + k + ChartWidth)Mod ChartWidth))) n = n + 1 j = (j + 10) Mod ChartWidth  Loop While n <=(200 − k)/10  NormAbsDiff = 100 * AbsDiff/(n * Abs(MaxSignal −MinSignal))  If NormAbsDiff <= MinAbsDiff Then MinAbsDiff = NormAbsDiffMaxK = k  End If  k = k + 1 Loop While k <= Period + Range If MaxK >= 40And MaxK <= 150 Then Period = MaxK Predict = SigBuf(SigRefIdxBuf((CurrJ− Period + ChartWidth) Mod ChartWidth)) Diff = 100 *Abs(SigBuf(SigRefIdxBuf(CurrJ)) − Predict)/Abs(MaxSignal − MinSignal) IfMinAbsDiff <= 20 Then  ProgressBar1.Value = MinAbsDiff Else ProgressBar1.Value = 20 End If End Function

In this program code, the variable “i” represents a counter or index tothe data sample being processed. The variable “Range” represents thesearch range that is to be analyzed. If the period of the physiologicalcycle has already been determined (i.e., from a prior execution of thisprogram code), then the variable “Period” comprises the detected period.If the period has not yet been determined, then the variable “Period” isset to a default value representative of a normal respiration cycle(e.g., the number of data points in a normal breathing cycle, which isapproximately 95 data samples in an embodiment of the invention whereapproximately 200-210 data samples are obtained over an approximately 7second time period). The variable “MinAbsDiff” is the minimum absolutedifference value over the search range. The variable “Diff” represents acomparison between the actual value of a next data sample and theexpected value of that next data sample.

The variables “j”, “StarLT”, and “CurrJ” are counters or indexes intothe data samples being processed. The variable “k” is a counter to thesearch range. The variable “MaxK” represents the position in the searchrange having the minimum absolute difference value. The variable“AbsDiff” maintains the sum of the absolute difference values foroverlapping data samples. The variable “NormaAbsDiff” is the averageabsolute difference value for a particular position in the search range,which is represented as a percentage value. The variable “n” is used totrack the position of the data samples relative to the search rangewhich is represented as a percentage value. “Predicf” is the predictedvalue that is returned by this program code.

The variable “MinAbsDiff” is initialized to a high value so that so thatany subsequent absolute difference value will be smaller than theinitialized value. In an embodiment, the set of data samples beingprocessed comprises 200 data points. Thus, in this program code, thevariable “StartJ” is initialized back 201 data samples. The variable“CurrJ” is initialized back one data sample. Because a circular array isbeing used, the “BufLength” variable is referenced during theinitialization of both “StarJ”and “CurrJ”.

The outer Do loop moves the current and preceding sets of data samplesrelative to each other. The outer Do loop is active while the variable“k” indicates that the program code is processing within the searchrange. In an embodiment, the search range is initially set at threepositions to either side of a predicted position. The predicted positionis based upon the period obtained for an immediately prior execution ofthe program code. If the program code has not been executed immediatelyprior, then a default period value is used. If an acceptable minimumabsolute difference value is not found within this search range, thenthe search range can be expanded to, for example, 50 positions to eitherside of the predicted position.

The variable “j” is initialized to the “StartJ” value. The variables“AbsDiff” and “n” are also initialized prior to execution of the innerDo loop.

The inner Do loop performs the computation of the absolute differencevalues between the present set and prior set of data samples. Thevariable “AbsDiff” maintains the sum of the absolute difference ofvalues for overlapping data samples being compared. Note that the numberof data samples being analyzed to determine the absolute differencevalues varies based upon the position in the search range beingprocessed. This results because different positions in the search rangehas different numbers of data samples that overlap with the previous setof data samples being compared. In the embodiment of this program code,the absolute difference function is computed using every 10 ^(th) signalsample point, i.e., a subsampled subtraction is used. Because a circulararray is being used, the “Chartwidth” variable is referenced during thecalculation of “AbsDiff”.

The variables “MaxSignal” and “MinSignal” indicate a maximum and minimumrange for signal values that have previously been sampled. These valuescan be established, for example, during a learning period for the systemin which data samples are obtained for a plurality of respiratorycycles. The “NormAbsDiff” variable holds the average absolute differencevalue represented as a percentage value based upon the “MaxSignal” and“MinSignal” values.

If the “NormAbsDiff” value is less than or equal to a previouslyestablished “MinAbsDiff” value, then the “MinAbsDiffr” variable is setto the “NormAbsDiff” value. The “MaxK” variable is set to the value of“k” if the “MinAbsDiff” value is reset. The variable “k” is thenincremented, and if the “k” value is still within the search range, thenthe program code returns back to the beginning of the outer Do loop.

The result of this program code is a candidate minimum absolutedifference value and a candidate position for the minimum absolutedifference. The MaxK value is compared to pre-defined threshold valuesto ensure that it falls within a correct range of values for thephysiological activity being processed. Thus, in an embodiment, the MaxKvalue is tested to make sure that it is greater than or equal to 40 andless than or equal to 150. If the mark value meets the threshold range,then the variable “Period” is set to the “MaxK” value. The variable“Predict” returns the predicted value for the next set of data samplesto be processed. The variable “Diff” indicates the difference valuebetween the current data sample value and the predicted data samplevalue, and is represented as a percentage to the “MaxSignal” and“MixSignal” values.

In an embodiment, an image of a progress bar can be displayed tovisually indicate the periodicity of the signal samples. According tothe program code, if the “MinAbsDiff” value is less than or equal to a20% difference, then the visual progress bar is updated with thecomputed “MinAbsDiff” value. Otherwise, the visual progress bar displaysall other “MinAbsDiff” values that exceed a 20% difference as a defaultvalue of “20”.

FIGS. 6 a and 6 b depict an embodiment of a camera 108 that can used inthe present invention to optically or visually collect datarepresentative of physiological movement. Camera 108 is a charge-coupledevice (“CCD”) camera having one or more photoelectric cathodes and oneor more CCD devices. A CCD device is a semiconductor device that canstore charge in local areas, and upon appropriate control signals,transfers that charge to a readout point. When light photons from thescene to be images are focussed on the photoelectric cathodes, electronsare liberated in proportion to light intensity received at the camera.The electrons are captured in charge buckets located within the CCDdevice. The distribution of captured electrons in the charge bucketsrepresents the image received at the camera. The CCD transfers theseelectrons to an analog-to-digital converter. The output of theanalog-to-digital converter is sent to computer 410 to process the videoimage and to calculate the positions of the retro-reflective markers406. According to an embodiment of the invention, camera 108 is amonochrome CCD camera having RS-170 output and 640×480 pixel resolution.Alternatively, camera 408 can comprise a CCD camera having CCIR outputand 756×567 pixel resolution.

In a particular embodiment of the invention, an infra-red illuminator602 (“IR illurninator”) is co-located with camera 108. IR illuminator602 produces one or more beams of infrared light that is directed in thesame direction as camera 108. IR illuminator 602 comprises a surfacethat is ringed around the lens 606 of camera body 608. The surface of IRilluminator 602 contains a plurality of individual LED elements 604 forproducing infrared light. The LED elements 604 are arranged in a spiralpattern on the IR illuminator 602. Infixed filters that may be part ofthe camera 108 are removed or disabled to increase the camera'ssensitivity to infrared light.

According to an embodiment, digital video recordings of the patient in asession can be recorded via camera 108. The same camera 108 used fortracking patient movement can be used to record video images of thepatient for future reference. A normal ambient light image sequence ofthe patient can be obtained in synchronization with the measuredmovement signals of markers 114.

FIGS. 7 a and 7 b depict an embodiment of a retro-reflective marker 700that can be employed within the present invention. Retro-reflectivemarker 700 comprises a raised reflective surface 702 for reflectinglight. Raised reflective surface 702 comprises a semi-spherical shapesuch that light can be reflected regardless of the input angle of thelight source. A flat surface 704 surrounds the raised reflective surface702. The underside of flat surface 704 provides a mounting area toattach retro-reflective marker 700 to particular locations on apatient's body. According to an embodiment, retro-reflective marker 700is comprised of a retro-reflective material 3M#7610WS available from 3MCorporation. In an embodiment, marker 700 has a diameter ofapproximately 0.5 cm and a height of the highest point of raisedreflective surface 702 of approximately 0.1 cm.

FIG. 8 depicts an apparatus 802 that can be employed to manufactureretro-reflective markers 700. Apparatus 802 comprises a base portion 804having an elastic ring 806 affixed thereto. Elastic ring 806 is attachedto bottom mold piece 808 having a bulge protruding from its center. Acontrol lever 810 can be operated to move top portion 812 along supportrods 814. Top portion 812 comprises a spring-loaded top mold piece 814.Top mold piece 814 is formed with a semi-spherical cavity on itsunderside. In operation, a piece of retro-reflective material is placedon bottom mold piece 808. Control lever 810 is operated to move topportion 812 towards base portion 804. The retro-reflective material iscompressed and shaped between the bottom mold piece 808 and the top moldpiece 814. The top mold piece 814 forms the upper exterior of theretro-reflective material into a semi-spherical shape.

In an alternate embodiment, marker 114 comprises a marker block havingone or more reference locations on its surface. Each reference locationon the marker block preferably comprises a retro-reflective orreflective material that is detectable by an optical imaging apparatus,such as camera 108.

FIG. 11 depicts an embodiment of a marker block 1100 having acylindrical shape with multiple reference locations comprised ofretro-reflective elements 1102 located on its surface. Marker block 1100can be formed as a rigid block (e.g., from Styrofoam). Blocks made inthis fashion can be reused a plurality of times, even with multiplepatients. The retro-reflective elements 1102 can be formed from the samematerial used to construct retro-reflective markers 114 of FIGS. 7 a and7 b. The marker block is preferably formed from a material that islight-weight enough not to interfere with normal breathing by thepatient.

A marker block can be formed into any shape or size, as long as thesize, spacing, and positioning of the reference locations are configuredsuch that a camera or other optical imaging apparatus can view andgenerate an image that accurately shows the positioning of the markerblock. For example, FIG. 10 depicts an alternate marker block 1000having a hemispherical shape comprised of a plurality ofretro-reflective elements 1002 attached to its surface.

The marker block can be formed with shapes to fit particular body parts.For example, molds or casts that match to specific locations on the bodycan be employed as marker blocks. Marker blocks shaped to fit certainareas of the body facilitate the repeatable placement of the markerblocks at particular locations on the patient. Alternatively, the markerblocks can be formed to fit certain fixtures that are attached to apatient's body. For example, a marker block can be formed withinindentations and grooves that allow it to be attached to eyeglasses. Inyet another embodiment, the fixtures are formed with integral markerblock(s) having reflective or retro-reflective markers on thenl

An alternate embodiment of the marker block comprises only a singlereference location/reflective element on its surface. This embodiment ofthe marker block is used in place of the retro-reflective marker 406 todetect particular locations on a patient's body with an optical imagingapparatus.

Further details regarding camera 108, markers 114, marker blocks, orprocedures to optically measure physiological movements are described incopending U.S. patent application Ser. No. 09/178,384 and U.S. patentapplication Ser. No. 09/178,385, filed concurrently herewith, both ofwhich are hereby incorporated by reference in their entirety.

FIG. 12 is a block diagram that illustrates an embodiment of a computersystem 1900 upon which an embodiment of the invention may beimplemented. Computer system 1900 includes a bus 1902 or othercommunication mechanism for communicating information, and a processor1904 coupled with bus 1902 for processing information. Computer system1900 also includes a main memory 1906, such as a random access memory(RAM) or other dynamic storage device, coupled to bus 1902 for storinginformation and instructions to be executed by processor 1904. Mainmemory 1906 also may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby processor 1904. Computer system 1900 further includes a read onlymemory (ROM) 1908 or other static storage device coupled to bus 1902 forstoring static information and instructions for processor 1904. A datastorage device 1910, such as a magnetic disk or optical disk, isprovided and coupled to bus 1902 for storing information andinstructions.

Computer system 1900 may be coupled via bus 1902 to a display 1912, suchas a cathode ray tube (CRT), for displaying information to a user. Aninput device 1914, including alphanumeric and other keys, is coupled tobus 1902 for communicating information and command selections toprocessor 1904. Another type of user input device is cursor control1916, such as a mouse, a trackball, or cursor direction keys forcommunicating direction information and command selections to processor1904 and for controlling cursor movement on display 1912. This inputdevice typically has two degrees of freedom in two axes, a first axis(e.g., x) and a second axis (e.g., y), that allows the device to specifypositions in a plane.

The invention is related to the use of computer system 1900 fordetecting and predictively estimating physiological cycles. According toone embodiment of the invention, such use is provided by computer system1900 in response to processor 1904 executing one or more sequences ofone or more instructions contained in main memory 1906. Suchinstructions may be read into main memory 1906 from anothercomputer-readable medium, such as storage device 1910. Execution of thesequences of instructions contained in main memory 1906 causes processor1904 to perform the process steps described herein. One or moreprocessors in a multi-processing arrangement may also be employed toexecute the sequences of instructions contained in main memory 1906. Inalternative embodiments, hard-wired circuitry may be used in place of orin combination with software instructions to implement the invention.Thus, embodiments of the invention are not limited to any specificcombination of hardware circuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 1904 forexecution. Such a medium may take many forms, including but not limitedto, non-volatile media, volatile media, and transmission media.Non-volatile media includes, for example, optical or magnetic disks,such as storage device 1910. Volatile media includes dynamic memory,such as main memory 1906. Transmission media includes coaxial cables,copper wire and fiber optics, including the wires that comprise bus1902. Transmission media can also take the form of acoustic or lightwaves, such as those generated during radio wave and infrared datacommunications.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, a RAM, a PROM, and EPROM,a FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to processor 1904 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 1900 canreceive the data on the telephone line and use an infrared transmitterto convert the data to an infrared signal. An infrared detector coupledto bus 1902 can receive the data carried in the infrared signal andplace the data on bus 1902. Bus 1902 carries the data to main memory1906, from which processor 1904 retrieves and executes the instructions.The instructions received by main memory 1906 may optionally be storedon storage device 1910 either before or after execution by processor1904.

Computer system 1900 also includes a communication interface 1918coupled to bus 1902. Communication interface 1918 provides a two-waydata communication coupling to a network link 1920 that is connected toa local network 1922. For example, communication interface 1918 may bean integrated services digital network (ISDN) card or a modem to providea data communication connection to a corresponding type of telephoneline. As another example, communication interface 1918 may be a localarea network (LAN) card to provide a data communication connection to acompatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 1918 sends and receiveselectrical, electromagnetic or optical signals that carry data streamsrepresenting various types of information.

Network link 1920 typically provides data communication through one ormore networks to other devices. For example, network link 1920 mayprovide a connection through local network 1922 to a host computer 1924or to medical equipment 1926 such as a radiation beam source or a switchoperatively coupled to a radiation beam source. The data streamstransported over network link 1920 can comprise electrical,electromagnetic or optical signals. The signals through the variousnetworks and the signals on network link 1920 and through communicationinterface 1918, which carry data to and from computer system 1900, areexemplary forms of carrier waves transporting the information. Computersystem 1900 can send messages and receive data, including program code,through the network(s), network link 1920 and communication interface1918.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Forexample, the operations performed by computer 110 can be performed byany combination of hardware and software within the scope of theinvention, and should not be limited to particular embodimentscomprising just a particular definition of “computer”. The specificationand drawings are, accordingly, to be regarded in an illustrative ratherthan restrictive sense.

1. A method of gating an application of radiation, comprising: obtaininga first set of data representative of a physiological movement of apatient during a first time period; obtaining a second set of datarelated to a measured physiological movement of the patient during asecond time period; comparing the first set of data with a second set ofdata; and gating an application of radiation to the patient based on aresult of the comparing.
 2. The method of claim 1, wherein the comparingthe first set of data with the second set of data comprises patternmatching the first set of data with the second set of data.
 3. Themethod of claim 2, wherein the first set of data and the second set ofdata are pattern matched using an autocorrelation function.
 4. Themethod of claim 2, wherein the first set of data and the second set ofdata are pattern matched using an absolute difference function.
 5. Themethod of claim 1, further comprising determining a degree of matchbetween the first set of data and the second set of data.
 6. The methodof claim 5, wherein the degree of match is determined based on asecondary peak value of an autocorrelation function.
 7. The method ofclaim 5, wherein the degree of match is determined based on a secondaryminimum value of an absolute difference function.
 8. The method of claim5, further comprising comparing the degree of match to a thresholdrange.
 9. The method of claim 8, wherein the physiological movement isconsidered deviated from a normal physiological movement when the degreeof match is outside the threshold range.
 10. The method of claim 8,wherein the physiological movement is considered substantially the sameas a normal physiological movement when the degree of match is withinthe threshold range.
 11. The method of claim 1, further comprisingpredicting a period of physiological movement during a third timeperiod.
 12. The method of claim 11, further comprising predictivelyactuating a gating system component based upon the predicted period. 13.The method of claim 1, further comprising determining a period of thephysiological movement.
 14. The method of claim 13, further comprisingdefining a treatment interval to apply the radiation to the patient. 15.The method of claim 14, wherein the treatment interval is defined byphase of a physiological movement of the patient.
 16. The method ofclaim 1, wherein the second set of data is obtained based on a datamodel of a physiological movement of the patient.
 17. The method ofclaim 1, further comprising determining a degree of deviation fromperiodicity of a physiological movement based on a result of thecomparing.
 18. The method of claim 17, wherein the gating comprisesapplying radiation to the patient when the degree of deviation fromperiodicity is within a prescribed threshold.
 19. A method for gating anexecution of a procedure, comprising: determining a variablerepresentative of a degree of completion of a cycle of a physiologicalmovement; and gating an execution of a procedure based upon thevariable.
 20. The method of claim 19, wherein the determining comprisescomparing a first set of data representative of the physiologicalmovement during a first time period with a second set of data related tothe physiological movement during a second time period.
 21. The methodof claim 20, wherein the comparing comprises pattern matching the firstset of data with the second set of data.
 22. The method of claim 21,wherein the first set of data and the second set of data are patternmatched using an autocorrelation function.
 23. The method of claim 21,wherein the first set of data and the second set of data are patternmatched using an absolute difference function.
 24. The method of claim19, wherein the procedure comprises an application of radiation.
 25. Themethod of claim 24, further comprising defining a treatment interval forapplying the radiation.
 26. The method of claim 25, wherein the gatingcomprises applying the radiation when the degree of completion of thecycle is within the treatment interval.
 27. The method of claim 19,wherein the variable has a range between 0° and 360°, with 0°representing a beginning of a physiological cycle, and 360° representingan end of a physiological cycle.